1. Field of the Invention
The invention is in the field of providing cathodic protection of metal structures, especially steel offshore platforms, by the use of sacrificial anodes.
2. General Background
Sacrificial anodes and/or impressed current anodes are used on most offshore steel structures to prevent or reduce seawater corrosion of the steel. Generally these anode systems must be installed during platform fabrication. Replacement while the structure is located in the sea is difficult and expensive because divers must be used and work in deep water must be limited because of the high cost and danger to the workmen. In an effort to provide adequate protection, many very large sacrificial anodes are required to protect a structure for a typical lifetime of 20-40 years. The additional weight and wave forces on the anodes can become quite significant.
U.S. Pat. No. 4,201,637, issued May 6, 1980, and based on an application filed Nov. 15, 1978, discloses an apparatus and method wherein the sacrificial anodes can be replenished periodically or continuously. Briefly, the method comprises feeding the anode in particulate form to a container located under the surface of the water and electrically connected to the structure to be protected.
Our invention provides another improvement in the means of providing anode material continuously to the structure to be protected.
Also, our invention provides an improvement over the apparatus and method disclosed in U.S. Pat. No. 4,201,637. This feature will be described in detail later in our disclosure.